Once you get higher than 8,000 feet, the human body can start to have a hard time dealing with the lack of oxygen. And the higher you go, the greater the risk that you might experience two of the most serious forms of acute mountain sickness—pulmonary and cerebral edema. Pulmonary edema attacks the lungs while cerebral affects the brain, and both can be fatal.
Signs of pulmonary edema include fatigue, trouble breathing, coughing, pink sputum and chest tightness. Early signs of cerebral edema, the more life-threatening of the two, include fatigue, vomiting, confusion, behavioural changes and a drunken stagger.
The first thing to do if you suspect you are suffering from either sickness is to tell someone to keep an eye on you, since your oxygen-starved brain may soon start failing you and it may become too late to help yourself. The best medicine is to drop to a lower elevation—at least 3,000 feet down—as quickly as possible. However, exertion may worsen your condition so, again, ask for help. (If bottled oxygen is available, you should use it.) Subsequent rest should prove helpful, though the drunken stagger may last for several days afterward.